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Wednesday, August 11, 2010

ABG interpretation made easy: Oxygenation

An arterial blood gas can help you determine how well patient is oxygenating. Essentially, all you have to do is memorize the following chart.

PaO2

SpO2

Normal

80-100

95-99%

Mild Hypoxemia

60-79

90-94%

Moderate Hypoxemia

40-59

75-89%

Severe Hypoxemia

< 40

< 75%

Oxygen Therapy. Using oxygen therapy to improve oxygenation. It generally involves inhaling an FiO2 greater than that which is contained in room air.

Fraction of Inspired Oxygen (FiO2). This is the percent of oxygen in the air inhaled. Room air contains 21% FiO2. Oxygen Therapy may supply an FiO2 from 22-100%, depending on the device used. To learn more, check out "Oxygen Therapy Made Easy."

Goal of Oxygenation. Most protocols now recommend the least amount of supplemental oxygen to maintain an SpO2 of 90% and a PaO2 of 60. For some patients with lung disease, lower SpO2s may be acceptable. For instance, with some cases of advanced COPD, an SpO2 of 88% may be acceptable.

Refractory Hypoxemia. Supplemental oxygen does not improve oxygenation levels. Or, increasing FiO2 does not result in an increase in SpO2 and PaO2. It's commonly described as an SpO2 of less than 60 despite receiving 100% FiO2.

Hypoxemic Respiratory Failure. Failure of the heart and lungs to oxygenate the blood despite the application of supplemental oxygen via oxygen therapy.

You don't necessarily need to use these formulas to see if patient oxygenating well, yet sometimes they can be useful. Especially for the more complicated cases, it helps to see the numbers and the trends.

Post originally published on 8/11/10 on respiratory therapy cave; updated by Rick Frea for accuracy and simplicity.
Further Reading

2 comments:

Just clarifying...in the middle of the page when the author writes that SpO2 is 90, then the SaO2 should be 60, he means PaO2, not SaO2. SaO2 - 30 = expected PaO2. This can be verified by clicking the link at the bottom of this page for the oxyhemoglobin dissociation curve.